Conventional technologies for delivering exogenous proteins from an extracellular environment across a membrane lipid bilayer into cells are limited by inefficient membrane penetration of proteins, especially large proteins.
Synthetic peptides based on structure and sequence of secretion signal peptides have been exploited as protein delivery carriers (see, U.S. Pat. No. 5,807,746; U.S. Pat. No. 6,841,535; U.S. Patent No. 2010/0197598). Similarly, synthetic lipid amphiphiles have been demonstrated as intracellular delivery vehicles for a variety of bio-active molecules (see, U.S. Pat. No. 6,726,894). However, transfection technologies based on such carriers require that peptides (see, U.S. Pat. No. 6,841,535; U.S. Pat. No. 6,780,846) as well as amphiphiles (see, U.S. Pat. No. 6,726,894) be maintained at high concentration for complex formation between a cargo substance and the carrier and for intracellular delivery of the complex. This poses a serious limitation in therapeutic applications because unbound carrier can associate non-specifically with extracellular substances. Although covalent linkage between a transfection vector and its cargo can be established through chemical modification, lack of reaction specificity poses the risk of rendering the cargo inactive. The covalent reaction may occur at a catalytic center of a cargo enzyme, or on a functional surface of the cargo protein leading to inhibition or inactivation of the cargo protein function. Also, lack of specificity in covalent linkage formation between a cargo molecule and a protein transduction domain may lead to a heterogenous distribution of cargo molecules linked to the transduction domain at different positions.
Use of proteins fused to a secretion signal peptide produced as a recombinant single polypeptide chain has not been exploited. This is because during maturation of such a protein in a cell, the secretion signal sequence is typically cleaved.